'61 Ampeg R12-R Hum

[ca7922303]

Here is some reading for you.
nosaj

Appreciate that. Back at it shortly.

[ca7922303]

Here is some reading for you.
nosaj

Ok, I've read it. Can't say that I can apply it to how to scope the signal from PI to speaker. Schematic is not great I don't think and not seeing anything online to show me how to scope signal from PI to speaker. I was able to get output at speaker @ 23.63 watts rms.

[Helmholtz]

I was able to get output at speaker @ 23.63 watts rms.

Do you see symmetrical clipping at the load?

[ca7922303]

Do you see symmetrical clipping at the load?

Wasnt using oscope(PC based,, trying to load a driver for it into a new computer). Used DMM for output test.

[ca7922303]

Do you see symmetrical clipping at the load?

Im reading online that some have replaced caps and tubes and still have hum too loud to be able to record. Wondering if anyone has a grounding scheme that might work. I'm reading that grounding was not great on these amps? Thanks.

[Helmholtz]

Do we even know if the hum is 60Hz or 120Hz?

[ca7922303]

Do we even know if the hum is 60Hz or 120Hz?

Sounds like 120hz to me after listening to two(2) audio examples of 60hz & 120hz. Don't have oscope driver installed yet to look at the hum on oscope. Out of town for weekend. Back on it Monday. Any help on it is appreciated.

[Leo_Gnardo]

hum too loud to be able to record. Wondering if anyone has a grounding scheme that might work. I'm reading that grounding was not great on these amps? Thanks.

True that best grounding techniques weren't employed on early Ampegs. There's a ground path that connects at one end to the power supply chassis ground, then a series of black jumper wires that eventually end at the input jacks. What I do is remove the jumper between the output tubes' cathode resistor/cap ground and the rest of the preamp. That often does the trick, providing ground for power at one end, and ground for preamp at the other. It's also good practice to have the power transformer hi voltage center tap soldered to the same ground point as the filter cap. Also make sure there's a good bond to the chassis there as corrosion often degrades that connection over 50-60 years. Also make sure input jacks are tightened down thoroughly.

[ca7922303]

True that best grounding techniques weren't employed on early Ampegs. There's a ground path that connects at one end to the power supply chassis ground, then a series of black jumper wires that eventually end at the input jacks. What I do is remove the jumper between the output tubes' cathode resistor/cap ground and the rest of the preamp. That often does the trick, providing ground for power at one end, and ground for preamp at the other. It's also good practice to have the power transformer hi voltage center tap soldered to the same ground point as the filter cap. Also make sure there's a good bond to the chassis there as corrosion often degrades that connection over 50-60 years. Also make sure input jacks are tightened down thoroughly.

Appreciate that. Will get back on it Monday. Thanks.

[ca7922303]

True that best grounding techniques weren't employed on early Ampegs. There's a ground path that connects at one end to the power supply chassis ground, then a series of black jumper wires that eventually end at the input jacks. What I do is remove the jumper between the output tubes' cathode resistor/cap ground and the rest of the preamp. That often does the trick, providing ground for power at one end, and ground for preamp at the other. It's also good practice to have the power transformer hi voltage center tap soldered to the same ground point as the filter cap. Also make sure there's a good bond to the chassis there as corrosion often degrades that connection over 50-60 years. Also make sure input jacks are tightened down thoroughly.

Can you verify I'm heading in the right direction. I believe you are saying to remove the grey wire connecting V5/V6 to board @ 25uF 50v cap?

[ca7922303]

[Leo_Gnardo]

Can you verify I'm heading in the right direction. I believe you are saying to remove the grey wire connecting V5/V6 to board @ 25uF 50v cap?

Good photo. The grey wire is of interest. What I don't see, is any other wire exiting that junction, headed for ground at the power supply end of the amp. Here's what I'd try. First follow all the jumpers beyond that grey wire & see if they're not grounded at the input jack, they likely are. Run your own wire from where that common ground junction for the 2 caps & 250R resistor - to a handy ground lug terminal on the filter cap can. Lift one end of the grey wire and run a test, better hum or no? At this point the grounds for the power end of the amp are brought to chassis at the filter cap, and grounds for the preamp meet the chassis at input jack, usually a workable solution. IF this doesn't improve things, or makes 'em worse then all you have to do is solder the end of the grey wire back where it was, and remove the ground jumper that you installed for this test.

[g1]

ca7922303
Your probe is pointing at the wrong end of that cap. The grey wire at the other end is the one Leo means. Otherwise, follow his instructions.

[ca7922303]

ca7922303
Your probe is pointing at the wrong end of that cap. The grey wire at the other end is the one Leo means. Otherwise, follow his instructions.

Yeah, I noticed that cap was the positive end, but pin 8 seem to me to go to that end

[ca7922303]

Good photo. The grey wire is of interest. What I don't see, is any other wire exiting that junction, headed for ground at the power supply end of the amp. Here's what I'd try. First follow all the jumpers beyond that grey wire & see if they're not grounded at the input jack, they likely are. Run your own wire from where that common ground junction for the 2 caps & 250R resistor - to a handy ground lug terminal on the filter cap can. Lift one end of the grey wire and run a test, better hum or no? At this point the grounds for the power end of the amp are brought to chassis at the filter cap, and grounds for the preamp meet the chassis at input jack, usually a workable solution. IF this doesn't improve things, or makes 'em worse then all you have to do is solder the end of the grey wire back where it was, and remove the ground jumper that you installed for this test.

If I've got it wired like you suggested, hum seems about the same. Anything else I could try? Input jacks are tight and jumper wire do end at input jacks. Haven't tried pt center tap to cap can ground point. Probably need help spotting that. Thanks